A construction machine such as a hydraulic excavator or a hydraulic crane is generally configured by an automotive lower travelling structure, an upper revolving structure mounted on the lower travelling structure to be capable of revolving thereon, and a working mechanism tiltably mounted on a front side of the upper revolving structure. The upper revolving structure mounts an engine on a rear portion in a revolving frame for driving a hydraulic pump, and mounts a cab, a fuel tank, an operating oil tank and the like on a front side in the revolving frame.
Here, a diesel engine is generally used as an engine that is a prime mover of a hydraulic excavator. There are some cases where harmful substances such as particulate matter (PM) and nitrogen oxides (NOx) are contained in an exhaust gas discharged from such a diesel engine. Therefore, the construction machine is provided with an exhaust gas purifying device in an exhaust pipe forming an exhaust gas passage of the engine for purifying an exhaust gas therein.
The exhaust gas purifying device is configured by including an oxidation catalyst (for example, diesel oxidation catalyst, referred to as “DOC” for short) for oxidizing and removing nitrogen monoxides (NO), carbon monoxides (CO), hydrocarbon (HC) that are contained in an exhaust gas, and a particulate matter removing filter (for example, diesel particulate filter, referred to as “DPF” for short) that is arranged downstream side of the oxidation catalyst for trapping and removing particulate matter in the exhaust gas (Patent Document 1).
Incidentally, in the particulate matter removing filter, the particulate matter is accumulated therein following the trapping of the particulate matter, which might cause the filter to be clogged. Therefore, it is necessary to remove the particulate matter from the filter in a point where a predetermined amount of the particulate matter is trapped for regenerating the filter. This regeneration of the filter can be performed in such a manner that fuel injection for regeneration treatment called “post injection” is performed to increase a temperature of an exhaust gas for burning the particulate matter that is accumulated in the filter.
On the other hand, when the regeneration treatment is executed in a point where the particulate matter is excessively accumulated in the filter, the temperature of the exhaust gas rises to be excessively high (a combustion temperature of the particulate matter is excessively high), which might possibly cause the filter to be melted and damaged. Therefore, the conventional art is configured such that a trapping amount of the particulate matter trapped in the filter is estimated, and, based thereon the regeneration treatment is executed before the estimated trapping amount becomes excessively large.
More specifically an emission amount (generating amount) of particulate matter that is discharged from the engine is estimated based upon a rotational speed of an engine, a fuel injection quantity and the like, and the regeneration treatment is executed at the time the estimated amount reaches a preset threshold value (Patent Document 2 and Patent Document 3).
Following an elapse of driving time, substances other than the particulate matter that has been burned and removed by the regeneration treatment, that is, ashes contained in engine oil, fuel or the like, which have not been burned or removed by the regeneration treatment, are accumulated in the filter. The other conventional art is configured such that an amount of the above ashes accumulated in the filter is estimated based upon the number of times by which the regeneration treatment has been executed, and the regeneration treatment is executed based upon the estimated amount of the ashes together with the amount of the particulate matter (Patent Document 4).